1. Field of the Invention
The present invention relates to a method of discriminating images. More particularly, the invention relates to a method of image and pattern recognition using a computer.
2. Description of the Relevant Art
Computerized identification systems are useful in a variety of applications. Products in a supermarket are branded with a barcode, the universal product code (UPC), that represents a ten digit number. A product UPC may identify the manufacturer and item number, which are correlated in a database to the product's price. Barcodes may be printed on a variety of surfaces and in a range of sizes. A laser scanning system is often used to recognize bar codes. Accurate readings may be obtained despite partial obscurement and nonuniform orientations. The barcode system is limited. The widths and spacing of a series of bars within a code represents a number. Thus, an accurate knowledge of the widths and spacing of the series of bars is crucial for accurate readings. As a barcode decreases in size, the bar widths and spaces can be obscured, because of resolution limitations.
Dot patterns may have advantages over barcode systems. FIG. 1 depicts a 5×5 dot pattern. Dots may be easier to make via photolithography, a process sometimes employed in making sensors. Additionally dots can be easily recognized in an image even if they are very small. Due to resolution limitations, as barcodes decrease in size accurate recognitions become more difficult. The dot pattern in FIG. 1 may not be a robust image identification system alone. The pattern can be rotated, flipped, and/or positioned upside-down. Patterns that are symmetric about a central axis may be misread if the pattern is rotated and/or mirrored.
FIG. 2 depicts two dot patterns with dots arranged in “M” and “W” formations with alignment markers positioned outside the patterns. Without the alignment markers, the patterns may become indistinguishable if one of the dot patterns is rotated 180 degrees. A similar situation arises if the dots in the pattern are arranged to resemble a “6” or a “9”. Some identification systems position an additional dot or line as an alignment marker to facilitate identification of patterns.
FIG. 3 depicts dot patterns with a single central alignment mark and a secondary off-center alignment mark. Without secondary alignment marks, the patterns are indistinguishable if one of the dot patterns is mirrored. Failure of an image recognition system may occur if a pattern with a single central alignment dot is mirrored, particularly if an alignment mark is positioned along an axis of symmetry.
FIG. 4a depicts dot patterns that appear identical if the unfilled dots are ignored or not detectable when one pattern is rotated 180 degrees. Often only dots that produce a signal are detectable by a detector; and so when attempting to recognize a pattern, two patterns that may not appear identical if all dots are detectable will appear identical due to the detector used. In FIG. 4b, mirroring may cause two distinct patterns to resemble each other. The addition of a second alignment dot does not aid in distinguishing the rotated or mirrored pattern. While individuals may be able to distinguish between the rotated and mirrored patterns with two properly positioned alignment dots, a computer based recognition system may have difficulty with only two alignment marks. In a computer based recognition system, the alignment marks, may be identified first and then the dot patterns may be identified. This may be a source of some of the difficulty a computer-based system may encounter with only two alignment dots. While the angle of an array may be determined with two alignment dots, the mirroredness of an array can not be determined. The system may incorrectly identify patterns without information regarding the mirroredness of an image. Additionally, with only two alignment dots/markers, the identification systems must search a large area around the alignment markers to find the complete array.